Ver1 is a simple linked list implementation.

Ver2 uses interfaces to print the linked list. We replace
printing a node with a method call, printNode. The body
of printNode is supplied by an object of a class which
knows the type of node that is to be printed. In this
case, a node containing String. An interface is defined
so that the print routine of LinkedList will allow any
class which has a printNode method to be passed to it.

Ver3 uses interfaces to search a linked list. Again
an interface is defined for any class which has a
compareNode method. The class implements compareNode
for a specific kind of node, in our case, a node 
with String contents. 

This is a bit more sophisticated
than the printNode example since the constructor
of an object that implements compareNode takes a String
argument and remembers it. This String that will be compared 
against the String content of the LinkedListNode on which 
this method will be invoked.